Molten bath treating method and apparatus



Nov. 26, 1963 .1. E. DE vRlEs MOLTEN BATH TREATING METHOD AND APPARATUS Filed Oct. 19. 1960 E www Em VD mE// ATTORNEY United States Patent O 3,112,194 MLTEN BATH TREATENG METHD AND APPARATUS loseph E. De Vries, Elizabeth, NJ., assigner to Union Carbide Corporation, a corporation of New Yorlr Filed st. i9, 1966, Ser. No. 63,627 9 Claims. (El. FiS-Sl) This invention relates to a method and apparatus for directing a flow of gas, or gas and lluid, onto the slag covered surface of a molten bath in a metallurgical furnace for treating the bath.

The use of oxygen or other gases lfor treating steel while still in the open hearth or electrical furnace, has long been recognized. While the following discussion will be limited to the use of oxygen as the treating gas, nosuch llimitation is intended since any number of gases may be handled by the disclosed device. lt has been generally accepted in `the industry, and is becoming more Widely practiced, that the introduction of oxygen and/or other fluids directly into the molten bath not only effectively reduces the required refining period, but also provides a higher quality of finished metal product.

One of the essential problems related to the injection of oxygen into a molten bath stems from the conception that, in order to function properly, the oxygen must be delivered to the bath at a `suliicient velocity to penetrate the slag accumulation which normally lies on the bath surface. One method of accomplishing this is to utilize a sufficient gas pressure that the high velocity fluid stream or streams penetrate the slag and are forceably injected into the bath. it has been found that such streams may take the form of a plurality of small divergently directed jets, or may even constitute a single large diameter stream. ln either instance, the primary purpose is to cause the oxygen to penetrate the slag layer and impinge on the bared molten surface; this is contrasted with the present invention which relies on the production of an oxygen flow having a very high angular velocity and a relatively low axial component such that the slag is urged into a circulatory motion rather than merely being penetrated by the impinging fluid.

` Usually, in prac-tice a lance for intr'oducing oxygen or other treating material is positioned with the discharge nozzle a :relatively short distance from the intensely hot bath surface in order to take full advantage of the high Velocity of the fluid being delivered. This, of course, results in considerable bath agitation, with particles off molten metal and slag being splashed violently about. Many of these particles, of course, strike and adhere to the lance outer surface where a metallic build-up gradually forms especially in the vicinity of the lance nozzle. It has been found that one oi the most practical methods for protecting the lancefrom intense furnace heat is to adequately cool the apparatus preferably with a circulatory coolant system. Ey such means, water under pressure is directed through the lance and especially through the forward exposed nozzle portion, to draw eti as much heat as possible. On the otl er hand, there is no generally accepted practical method for minimizing the damaging splash ellects either to the lance or to the furnace walls.

It is therefore an object of the present invention to provide a lance nfor introducing oxygen and/ or other fluids into a molten bath in such manner as to limit the amount of splash resulting from such introduction and thereby extend the usable life of the lance, and the exposed interior surfaces of the furnace.

A further object is to provide an apparatus for delivering a circulatory, tornado-like stream of fluid onto a molten slag covered bath to outwardly displace slag accumulations ytoward the furnace walls and thereby facilitate impingement of said fluid onto the exposed bath surface.

@l ld @d Patented Nov. 26, i963 ICC Another object is to provide a method for introducing a low Velocity stream of treating material to a molten bath surface in conjunction with a second stream having high rotational velocity.

Still a further object is to provide a method for introducing a fuel gas into the evacuated center of a rapidly rotating gas stream.

In the drawings:

FlG. l is a ver-tical cross-sectional view of a lance embodying the present invention;

FIG. 2 is an enlarged View in cross-section of ano-ther embodiment of the lance nozzle;

FIG. 3 is a View in cross-section taken along line 4 4 of FlG. l; and

FIG. 4 is a View in cross-section taken along line 5-S of FlG. 1.

In brief, the apparatus of the invention provides an elongated lance adapted for insertion through the shell of a metallurgical furnace to direct a swirling stream of fluid onto a slag covered, molten bath surface for the purpose of exposing said surface so that the fluid stream may impinge directly thereon. The lance comprises a plurality of concentrically positioned tubes of different diameters so disposed as to define concentric annular passages therebetween. A manifold fixed to the upper end of the respective tubes provides a closure for introducing additive fluids to be injected into the bath, and also provides means for directing coolant uid into and out ofthe lance. A nozzle assembly positioned at the `forward end of said tubes, includes a vortex chamber in which oxygen and/ or other fluids being utilized inthe bath treating process may l be formed into a swirling mass, and thence ejected from the nozzle discharge toward the bath surface as a rotating tornado-like stream having a partially evacuated center.

Referring to FlG. l, a lance embodying the principles of this invention is shown at lil and includes a central conduit 12| for injecting a uid, such as natural gas, or alterna-tively, a comminuted treating material, into the molten bath. To simplify the .following discussion, oxygen will be referred to as the addtive material. Concentrically disposed, elongated tubes ld, lo and lli are enclosed at the top end by a manifold 2li having lateral openings provided for receiving flexible conduits whereby oxygen or other treating gases may be directed into, and coolant fluid may be circulated through, the lance. The central conduit l2 is positioned at the manifold upper surface by a threaded coupling 2.2 also adapted for connection to a fluid source. ln operation of the lance, the central conduit 12 may also provide a vacuum tap into the vortex chamber 32.

The lower ends of the respective concentric tubes are provided rwith a nozzle suitably connected to define passages for receiving coolant and additive material. As shown in FlGS. 1 and 2, the nozzle comprises essentially a cylindrical core piece 3d into which an elongated vortex chamber 32 is fonmed, preferably coaxial with the lance. .A passage 3d extending through the rear wall of said core piece is communicably joined to the lower end of conduit l2. whereby additive materials such `as powdered desulphurizing or deoxidizing agent, or fuel gas may be injected into chamber 32. The chamber itself is preferably formed with the rear wall 53, and cylindrical side walls which terminate at a rather yforward discharge opening 36 at the nozzle iace. ln normal operation, this face is positioned as close as possible to the Imolten bath surface and is thereby subjected to severe wearing conditions as a result of furnace heat and rnetal splash as 3. fluid from the annular passage 43, and as shown, surrounds the upper portion of the `core piece. Means for introducing the oxygen, such as a number of laterally projecting ports 42, 44, 46 and 48j, communicate the accumulator chamber 46 with the central vortex chamber These lateral ports constitute an important feature of the invention, as they are so disposed in relation to chamber 32 that `high velocity oxygen streams issuing therefrom are guided by the vortex chamber walls and thus swirled about to form a tornado-like stream of oxygen in `which a partially evacuated center is established. This stream, on issuing fro-m the `chamber discharge port 36, will be possessed of sufficient rotational and axial velocity that the central evacuated portion will tend to .maintain the swirling motion as the gas approaches and strikes the slag covered bath surface.

An alternate embodiment of the nozzle portion of a lance is illustrated in FEG. 2 wherein the central core piece 36' is substantially as described in respect to the nozzle in FiG. 1 including the oxygen ports 42', 44', 46 and 4 which are directed into the central vortex charnber 32. Said chamber as shown is substantially cylindrical, with rear .wall 33 oppositely positioned from a discharge opening 36'. A longitudinal portion of said chamber, rearwardly adjacent the discharge opening, is provided with an outwardly flared surface 39. A nozzle of this type is primarily adapted for introducing a flow of oxygen or similar treating gas to the bath with no further additive incorporated in the fluid stream.

Due to the tornado-like characteristics of the issuing stream, the center portion `will achieve a varying degree of vacuum. It may thereby be seen that powdered additive material or a treating gas, introduced to the upper end of chamber 32 through passage 34, will be drawn downwardly and thence carried toward the nozzle discharge port within the central low pressure section.

In accordance with the present invention and referring particularly to FIGS. 1 and 4, the laterally disposed, constricted passages 42, 44, 46 and 4S (only 44 being here shown in FIG. 4) open into the rear portion of chamber 32, and are preferably biased toward the `discharge opening 35 to provide the entering oxygen streams with ya velocity component parallel to the longitudinal axis of the chamber. The biasing angle A may be between about 7 and 83 degrees, but is determined primarily such that the entering oxygen streams, on striking the cylindrical side walls of chamber 32, will have adequate opportunity to form into the desired swirling motion `and thereby become consolidated into a unitary mass prior to discharge from the nozzle face. It has been found by way of illustration, that `for a cylindrical chamber having a diameter of about 21/2 inches, a length of 11 inches is adequate to establish the desired tomado-like stream, when the biasing angle is approximately As seen in FIG. 4, the respective lateral ports (44) terminate substantially tangential to the Wall of chamber 32 whereby an oxygen stream, on entering said chamber, will be immediately guided against the cylindrical wall and thus initiated to the swirling motion. While the respective ports are shown in FIG. 4 as spaced approximately 99 apart, this is not an essential requirement; the actual number and disposition of said ports is primarily a function of the amount of oxygen to be delivered, and the available back pressure on the gas for making such delivery. Also, while the ports are shown in FIGS. 1 and 2 as being longitudinally positioned along the Wall of chamber 32, the desired circulatory flow may also be obtained by other means, such as a single ring of ports disposed near the upper end of the chamber.

The oxygen ports in the present embodiment preferably enter chamber 32 toward the rear wall 33 and are, as shown, longitudinally spaced along the chamber Wall to provide uniformity of ow to the swirling gas. While, as previously mentioned, it is preferable to direct the entering oxygen streams tangentially along the vortex chamber wall; from a practical point of View, this is not always possible. Tiercfore, it is only necessary in determining the angle of the entering oxygen streams, to assure that the respective ports do not come too close to a radial relationship ywith the chamber longitudinal axis. This will preclude the streams conflicting with each other, a condition which would tend to hamper or even prevent the formation of the tornado-like oxygen flow.

For achieving a high velocity, the oxygen ports are preferably formed with a rather small diameter or jet configuration in relation to the discharge opening 36 so that the forward impetus provided the gas on entering the vortex chamber 32 ywill maintain the swirling motion. Should the discharge velocity be too low at the lance face thereby minimizing the center vacuum, there will be a tendency for the issuing tornado-like gas stream to collapse prior to reaching the bath surface and thereby be rendered substantially ineffectual for displacing slag. It has been found, for instance, that the axial flow rate of oxygen at the discharge opening 36, with respect to the lance axis, may be as low `as about 10) feet per second while the angular component is about 3500 radians per second; this is contrasted with the normal injection velocity in other lances of from 500 to about 1060 feet per second, with zero angular velocity.

Again referring to Fla. l, coolant fluid, generally a liquid `and preferably water, is introduced to the upper end of the lance through the manifold 2t) and conducted forward to the nozzle end by way of annular passage 5S. The lower end of said passage terminates at the rear face 52 of the core piece into which surface coolant channels 54 are formed. Said channels extend longitudinally of the core piece, and outwardly adjacent the central vortex chamber. The respective channels 54 communicate with an annulus 56, the lower surface of which constitutes the rear surface of the nozzle forward face. It is this face portion that is generally subjected to the severest damaging influence of both furnace heat and metal splash.

The annular chamber 56 is formed with `a curved lower surface to reduce the amount of fiuidturbulence caused by the downward flowing coolant while entering said chamber, and thence being diverted into the outer annular passage 58. Passage 58, as seen in the gures, is defined by the adjacent cylindrical walls 33 and 6d, rearwardly extending from the nozzle forward end. Heat from the lance outer surface is dissipated by the sweep of coolant along the outer walls of passage 53 and, as previously mentioned, by passing the coolant at a relatively high velocity, there will be less opportunity for formation of a steam layer on the inner wall.

To achieve a more efficient cooling, it has been found that the presence of a baffle in passage 53 to limit the cross-sectional area of the annular' passage, provides the wat; flow with increased velocity and consequently greater heat transfer capacity. One embodiment of a baiiie adaptable to the invention comprises a formed helix 64 disposed in said passage to define a circuitous channel. The baille itself need not extend the entire length of the lance and is preferably confined to the nozzle lower section where cooling is most desirous. While the bale 64, as shown, may constitute a single length of wire or rod having a diameter approximately the size of the passage opening, it has been found that other suitable means may be utilized to restrict the open area of passage 58 and thereby achieve the necessary increased flow velocity. After passing the length of passage 58, the cooling fluid may be discharged through an appropriate outlet in manifold 26 to a connecting hose.

Another useful aspect of the lance stems from employment of the apparatus, as shown in FIG. l, in directing a stream of fluid such as natural gas, toward a molten bath for heating purposes. In such an instance, the center tube 12 will conduct a ow of combustible gas axially into the chamber 32 and thence into the evacuated center of the oxygen stream.

The resulting gas flame, on ignition, will then be surrounded by the swirling oxygen which, as previously mentioned, functions to displace slag toward the furnace walls and expose the bath surface. An added advantage found in this embodiment of the lance is that the walls of chamber 32 are maintained relatively cool by Ithe rapidly flowing oxygen in spite of the central gas flame, since the flame never actually contacts the walls and is effectively insulated by the surrounding oxygen stream. It has been observed on close examination of the composite stream, issuing from the lance, that flame rings along the entire length of the vortex chamber 32 burn in a stable condition and leave as a rotating conical shape at the exit thereby `exhibiting the characteristic form of a true vortex or tornado.

Under normal conditions in which the lance is used to deposit an additive material such as a powdered desulphurizing agent for treating purposes, the agent may be controllably metered into conduit l2 through the manifold 2f?. During an exemplary test, made in conjunction with a typical steel melting furnace, oxygen was directed into the lance at a rate of approximately 15 cubic feet per hour. `On being introduced to the vortex chamber, the oxygen streams were lguided in a spiral path to form the tornado-like swirling mass having a center portion in which the `degree of vacuum was determined to be approximately 15 inches of mercury. In subsequent tests with the same lance, the center vacuum was found to vary from between inches of water to 15 inches of mercury as the rate of oxygen flow increased from 2000 to 15,000 cubic feet per hour. It is therefore understandable that the formation of a vacuum center in the tornado-like flow of `oxygen is dependent on both the amount of oxygen used and also upon the angle at which oxygen streams enter the vortex chamber.

In either event, the molten, slag covered bath will receive a circulatory flow of oxygen having two essential purposes. One being to urge the slag into a rotational movement by virtue of the rotative component of oxygen ow, thereby exposing the bath surface. Secondly, to impinge a relatively soft or low velocity flow of fluid onto the exposed surface -such that a rather placid atmosphere may be maintained with only a minimum of splash resulting. It has been found for instance that with an outer tomado-like flow of oxygen swirling at a rate of about 3500 radians per second, the flow of additive fluid was introduced at between to 300 feet per second and consequently effected only a slight degree of agitation on the exposed bath surface.

Further tests conducted on a lance as here disclosed, have indicated that using an oxygen back pressure of approximately 30 p.s.i., and with the oxygen ports disposed at an angle A of about 15 from the lance axis, a tornadolike flow will issue from the discharge opening having a radial velocity in the vicinity of about 3500 radians per second. ln effect, the axial component of the discharging stream has been greatly reduced to minimize bath splash, but the radial or circulatory component has been substantially increased for the purpose of urging the bath slag into a generally rotary motion.

A still further useful aspect of the invention to achieve an improved treating process, resides in the use of a flow of water which is introduced into the oxygen stream or alternatively into the stream of additive material. This may be accomplished by introducing a flow of water through a suitable inlet connection at the rear end of the apparatus or directly into the central additive tube. It has been found that the water entering the forward, tubular chamber, tends to coat the walls and thus prevent thermal deterioration. lt has also been found that discrete amounts of water injected into the furnace reaction zone will have the desirable effect of reducing the amount of smoke which is produced by the process while not deterring from overall efficiency. In the latter instance, it has been found that the amount of water with respect to the amount of oxygen injected into the furnace may be in the ratio of about a half pound of water to a pound of oxygen. While the addition of water in itself has been previously employed as a smoke deterrent, the effectiveness of such addition has been limited by the usually inferior means of injection. I have found that by introducing the water in the form of droplets such as produced by injecting the water flow into the center of the swirling oxygen stream, the degree of smoke resulting from the treating process may be reduced by at least percent.

It is readily appreciated, then, that the hereindescribed lance affords not only a safer method for treating a molten bath, but it also assures a prolonged apparatus life since the detrimental effects of heat and metal splash to both lance and furnace have been greatly reduced. Use of the lance also affords a novel means for introducing a fuel gas or powdered additive to the bath thereby making the lance itself a highly desirable tool in the refining of molten metals. It is understood with respect to the present disclosure that certain modifications and changes might be effected in the apparatus and process without departing from the spirit and scope of the invention.

What is claimed is:

1. Process for chemically treating a slag covered molten bath with a composite stream of ffuid which comprises: directing a high velocity flow of an additive fluid to an elongated chamber, forming said flow against the chamber walls into a swirling stream having an evacuated center, introducing to said center a iluidized flow of a second additive material in a direction substantially axially to the swirling stream to form an axial stream therefor, discharging the swirling stream together with the axial stream toward the bath surface whereby both the slag and the metal surface may be urged into rotative movement permitting said second axial stream to be deposited on said surface with a minimum of splash.

2. A process substantially as described in claim l wherein the swirling stream is oxygen and the axial stream consists of particles of a comminuted additive material.

3. A process substantially as described in claim l wherein the swirling stream is oxygen and the axial stream consists of a combustible gas.

4. Process for treating a slag covered molten bath with a composite stream of fluid which comprises: directing a high velocity flow of oxygen to an elongated cylindrical chamber, forming said flow into a swirling stream having a radial velocity not substantially less than 3500 radians per second to establish a low pressure center portion in said stream, introducing to said center portion a low velocity flow of additive fluid in a direction substantially axial to the stream, and discharging the swirling stream together with the additive fluid into the molten bath, whereby said stream on expanding will maintain the low pressure center portion and urge said slag and melt surface into a rotative movement thereby permitting the low velocity flow of fluid to be deposited thereon with a minimum of splash.

5. Process substantially as described in claim 4 wherein the additive fluid is a combustible gas.

6. A lance for discharging a swirling stream of treating fluid toward a slag covered molten bath to impinge said fluid against the bath surface, said lance having axially disposed elongated tubes defining a plurality of annular passages therebetween for separately conducting said fluid and a coolant material longitudinally through said passages, a closure for relatively positioning the upper extremities of said tubes in fixed relation and for providing said annular passages with flows of said fluid and said coolant material, a nozzle communicably engaging said tubes, said nozzle having an outer face exposed to the bath surface, fluid passages in said nozzle for circulating said coolant material, an elongated chamber extending longitudinally through the nozzle having a discharge opening terminating at the nozzle face, means for introducing a high velocity flow of treating fluid laterally into said chamber in a direction substantially tangential to the chamber wall whereby said fluid may be urged along said wall and formed thereby into a swirling stream prior to leaving the discharge port.

7. A lance for discharging a swirling stream of treating iluid toward a slag covered molten bath to irnpinge said fluid against the bath surface, said lance having concentrically disposed elongated tubes dening therebetween annular uid conducting passages for separately conducting said Huid and a coolant material longitudinally through the lance, a closure for relatively positioning the upper ends of said tubes in fixed relationship and for providingT said annular passages with flows of said fluid and said coolant material, the discharge end of said lance comprising: a nozzle having concentrically disposed cylindrical walls engaging the lower end of said tubes, the outer face of said nozzle exposed to the bath surf-ac means in said nozzle for circulating said coolant material, the inner of said cylindrical walls deiining an elongated vortex chamber extending axially of said nozzle, said chamber being rearwardly dened by a wall, a discharge opening in said chamber diametrically opposed to said wall and terminating at the nozzle face, lateral ports opening into said chamber and adapted to receive treating fluid from said iiuid conducting passage, said ports relatively disposed with respect to said chamber to impinge a high velocity How of said uid against the vortex chamber walls whereby said fluid may be guided into a circular path along said wall and thence consolidated 8 into a swirling mass as said fluid advances toward the chamber discharge port.

8. In a lance substantailly as described in claim` 7 wherein the nozzle portion comprises: a face exposed to the bath, passages for conducting said coolant fluid, an inner cylindrical wall defining a chamber disposed substantially axially of said lance, said chamber having a rear wall diametrically opposed from an opening, said opening terminating at the nozzle face, an accumulator chamber communicating with an annular passage for conducting said fluid, laterally disposed ports communicating said accumulator chamber with said vortex chamber for delivering high velocity flows of said uid to said vortex chamber in a direction substantially tangential to the cylindrical walls whereby said ows may be guided by said walls into a swirling stream and discharged toward the bath in a tornado-like stream.

9. A method substantially as described in claim l, in which the swirling stream is oxygen, and the axial stream consists of water.

References Cited in the le of this patent UNITED STATES PATENTS 774,93() Brown Nov. l5, 1904 1,748,750 Becket Feb. 25, 1930 2,644,746 Hauttmann a July 7, 1953 2,892,699 Austin et al lune 30, 1959 FOREIGN PATENTS 1,211,977 France Mar. 2l, 1960 

4. PROCESS FOR TREATING A SLAG COVERED MOLTEN BATH WITH A COMPOSITE STREAM OF FLUID WHICH COMPRISES: DIRECTING A HIGH VELOCITY FLOW OF OXYGEN TO AN ENLONGATED CYLINDRICAL CHAMBER, FORMING SAID FLOW INTO A SWIRLING STRAM HAVING A RADIAL VELOCITY NOT SUBSTANTIALLY LESS THAN 3500 RADIANS PER SECOND TO ESTABLISH A LOW PRESSURE CENTER PORTION IN SAID STREAM, INTRODUCING TO SAID CENTER PORTION A LOW VELOCITY FLOW OF ADDITIVE FLUID INA DIRECTION SUBSTANTIALLY AXIAL TO THE STREAM, AND DISCHARGING THE SWIRLING STREAM WHEREBY SAID STREAM ON EXPANDING WILL MAINTAN THE LOW PRESSURE CENTER PORTION AND URGE SAID SLAG AND MELT SURFACE INTO A ROTATIVE MOVEMENT THERBY PRMITTING THE LOWER VELOCITY FLOW OF FLUID TO BE DEPOSITED THEREON WITH A MINIMUM OF SPLASH. 